1. Field of the Invention
The present invention relates to a conveying machine, and more particularly to a conveying machine for circulatorily moving a plurality of carrier boxes on a looped route.
2. Description of the Related Prior Art
In recent years, a conveying machine for moving a plurality of carrier boxes laden with loads to deliver the loads to prescribed gathering units to sort the loads (which may be mails, for instance) has come into use.
FIG. 1 shows a plan of a schematic configuration of a conventional conveying machine 100 (a conveying machine for mails) according to the prior art, and FIG. 2, its front view.
Referring to FIG. 1 and FIG. 2, the prior art conveying machine 100 comprises a case 10, carrier boxes 20 and a guide rail 50.
FIG. 3, shows details of section E in FIG. 1. Referring to FIG. 3, the conveying machine 100 further includes a plurality of carrier trucks 130. The guide rail 50 is installed within the case 10, and formed in a loop shape having linear sections and curvilinear sections. The carrier trucks 130, supported by the guide rail 50, circulatorily travels on the looped route. The carrier trucks 130 are linked by joints 131 to constitute a chain conveyor 160.
The case 10 comprises a plurality each of sorting cases 11 and a feeding case 12. The sorting cases 11 have a plurality of gathering units 111 for gathering loads discharged from the carrier boxes 20. The feeding case 12 has a drop unit 13 for feeding loads to the carrier boxes 20 by conveyance by a belt 14. The gathering units 111 and the drop unit 13 are arranged in the linear conveyance part of the carrier boxes 20.
FIG. 4 gives a view in the direction of arrow F in FIG. 3. Referring to FIG. 4, the carrier boxes 20 hang from the carrier trucks 130.
Next will be described the operation of the conveying machine 100 configured as explained above.
The belt 14 of the feeding case 12 individually conveys loads (which may be mails, for instance) one unit at a time to the drop unit 13. Each load is dropped by the drop unit 13 into a prescribed one of the carrier boxes 20. A drive mechanism (not shown) of the chain conveyor 160 causes the carrier boxes 20 to be conveyed at a constant speed.
The carrier boxes 20 are partitioned to provide one compartment for each mail. The carrier boxes 20 convey mails, and discharge them, classified by destination, into respectively prescribed ones of the gathering units 111 of the sorting cases 11.
As is evident from FIG. 3, the carrier boxes 20 are arranged at equal intervals (L3=L4) in the conveying machine 100 described above. For this reason, the intervals between the carrier boxes 20 should be wide enough (intervals L4) not to let adjoining carrier boxes 20 interfere with each other in curvilinear sections of the guide rail 50. Therefore, even if the intervals are kept to the necessary minimum for the carrier boxes 20 not to interfere with each other in curvilinear sections, the intervals between the carrier boxes 20 will widen in linear sections (intervals L3). As a consequence, the mounting efficiency of the carrier boxes 20 would deteriorate and the density of conveyance decrease in linear sections.
Since the number of loads handled per unit length of time depends on the speed of conveyance of the carrier trucks 130 by the chain conveyor 160, the number of loads handled can be increased by raising the speed of conveyance. However, a higher speed of conveyance than a certain level would destabilize the actions to drop and discharge loads into and out of the carrier boxes 20 being conveyed at a constant speed and thereby deteriorate the reliability of load handling.
Slowing the speed of conveyance to stabilize the load dropping and discharging actions would substantially reduce the load handling capacity per unit length of time on account of the resultant low mounting efficiency of the carrier boxes 20 in linear sections.
As described so far, the conveying machine according to the prior art is incapable of stable load handling without sacrificing the efficiency of handling because the intervals between carrier boxes widen in linear sections and the density of conveyance of carrier boxes there is reduced.